Magnetic recording disk drives that use “shingle writing”, also called “shingled recording” or “shingled magnetic recording” (SMR), have been proposed. In SMR, the write head, which is wider than the read head in the cross-track direction, writes magnetic transitions by making a plurality of consecutive circular paths that partially overlap. The non-overlapped portions of adjacent paths form the shingled data tracks, which are thus narrower than the width of the write head. The data is read back by the narrower read head. The narrower shingled data tracks thus allow for increased data density. The shingled data tracks are arranged on the disk as annular regions or bands separated by annular inter-band gaps. When data is to be re-written or updated, all of the shingled data tracks that were written after the track being updated was written are also re-written. SMR is well-known in the art, for example as described in U.S. Pat. No. 6,185,063 B1 and U.S. Pat. No. 6,967,810 B2.
However, attempting to pack tracks very closely together risks the newly written track causing damage to the adjacent previously written tracks. Because of this risk, it is valuable to have a method of verifying data previously written on an adjacent track(s) in a SMR disk drive.